1. Field of Invention
This invention relates to tools for work on bicycles.
2. Prior Art
A typical mounting of a bicycle tire to its host wheel begins with pulling one side of a bicycle tire and its associated edge, or bead, over the rim sidewall, or flange, of the hosting bicycle wheel's rim all the way around the periphery of that rim. This places that side of the tire totally within the two inside faces of the rim's flanges. Cross sectional view of the rim (between two spokes) with this completed is FIG. 1. Locating the inner tube's air filler valve stem near the access hole provided for it in the wheel, the inner tube is then tucked into the space within the confines of the interior of the tire and between both inside faces of the wheel rim's flanges. Cross sectional view of the tire and wheel rim with this completed is FIG. 2. The second bead of the tire is then progressively pulled into the confines of the wheel rim's flanges in a way similar to that for the first tire bead. However, the tension on this second tire bead increases progressively as more of the bead is placed in the rim's interior to a point such that the grip of one's hands may be insufficient to pull the rest of the bead into the interior. A view of the progress to this point is FIG. 3.
Presently, the common method of placing the rest of the bead into the interior of the rim to complete the mounting of the tire is to employ several small levers, known as “tire irons”, or “tire levers”, to force the rest of the bead in. Tire irons are miniature pry bars that have one end flattened and smoothed for easy insertion between the tire and it's hosting rim, and the other end fashioned for use as a handle. U.S. patent No. D395,809 by William P. Brown, entitled “Tire Iron” shows the prior art of a highly ornate, but highly illustrative tire iron design. Though both ends were fashioned as ends to contact the tire and rim, and neither as a handle per se, the flattening of the ends illustrate the insertion and prying functions well.
The use of tire irons is conceptually straightforward. First one inserts a tire iron between the section of the rim's flange you want the tire bead to drop in behind and the bead of the corresponding segment of tire. Then using the rim's flange as a fulcrum, one pivots the iron in the rotational direction to bring the iron's handle end away from the center hub of the wheel, and away from the plane the wheel rim lies in, forcing the bead to follow a circular path up and into the area between the inside faces of the rim's flanges. As soon as the inclination of the iron is sufficiently steep, the tension on the tire bead draws that section of the tire off the iron and into the confines of the rim. One then continues on to the next section of tire still outside the rim. One would continue in this fashion until all the tire is on the rim.
However, on most actual tire and rim combinations, due to the high and increasing tension in the tire bead from the point of progress depicted in FIG. 3 on, there is a required sequence to how one places the irons as you advance that portion of the tire yet outside the rim into the rim. That sequence begins by inserting a tire iron between the rim and the yet unseated portion of the tire, such that the tire iron is not situated in the middle of the yet unseated portion of the tire, but instead close to either end where the bead transitions from being off the rim to being on the rim. Using the iron at either end insures the bead begins it's travel close to the rim and therefore close to the tip of the iron. This utilizes the mechanical advantage a tire iron is meant to provide. If instead one starts at the middle where the tire bead is stretched between the transition points of the bead as mentioned above, the bead begins it's travel much further away from the fulcrum that is the wheel rim flange's edge (and so closer to the handle end of the iron) than in the previous case, thus negating the mechanical advantage the use of a tire iron (a lever) was to provide in the first place.
Even if the just outlined sequence is adhered to, the tire iron approach has significant problems.
As was mentioned, placing the second tire bead into the bicycle rim can at first be done by hand. As one progresses, it gets more difficult and at some point requires the use of a tool to place the bead within the confines of rim's flanges. One can advance additional lengths of the remaining unmounted bead onto the rim with the use of a single tire iron applied progressively to the remaining sections of bead. However, there comes a point for many tire and rim combinations where the tension in the bead becomes so great that a section of bead successfully levered inside the rim's flanges will pull right back out when the lever is removed. To get such a section of bead to remain placed in the rim, common practice is to commit the lever that put it there as a restraining device. This is done by not removing the lever once it has placed this section of bead, but instead holding it fixed there in its finished position. To progress in the mounting of the tire from this point, one needs to employ additional levers. However, once two irons are employed in this function you need either an assistant or some kind of lever holding fixture to free up another hand so one can continue since to keep an iron in a bead restraining position it must be held. Frequently, three or more irons are needed to get the last bead section to snap into place on the rim. This makes the field use of irons to complete a tire installation with these types of tire and rim combinations impractical.
Another problem one encounters in levering the tire into the rim is that irons tend to slip from their desired position on the rim's edge. Common tire irons are made smooth on their exterior to facilitate easy insertion between the tire and rim, and reduce abrasion to the tire. However, the resulting slipperiness also makes it difficult to keep the iron positioned on the rim where you want it to stay. This tendency increases as the tension in the bead increases as it does toward the end of the tire installation. If the iron slips out from between the tire and the rim, the levering action is not completed, and the tire snaps back to where it was. Also, if one pushes the iron too far into the area between the rims, inner tube penetration (puncture & ruination) can easily result. This particular problem of going too far in is greatly aggravated by the fact that the force exerted radially on the iron (using the point of pivot as a radial origin) by the tire bead changes direction from outward to inward as one passes through the point where the iron is horizontally positioned, that is, parallel to the axle of the hub of the wheel. Keeping the iron from sliding on the rim's edge during that quick transition can be very difficult.
An approach to the mounting of tires to their rims that does not use conventional tire irons is put forth in U.S. Pat. No. 3,771,581 by George A. Johnson, entitled “TIRE IRON” issued on Nov. 13, 1973. The device described therein is basically a rod with a handle end and a grooved end, the rod meant to be kept essentially perpendicular to the outside surface of the rim as it is driven along by impacts to its side such as could be delivered by a hammer, and guided by both the wheel rim placed in the groove of the tool and by the hand not doing the hammering. This device, however, has the drawback that its use requires maintaining a necessary angle between the axis of its handle and the rim's flange, which would be difficult as the device is being hammered. Another drawback this device suffers from is its undesirable but unavoidable effect of delivering a twisting force to the wheel rim that could be sufficient to bend it. The source of the twist is the impact delivered to it at one end whilst the other is held relatively stationary by the user's hand.